ONE reason America’s immigration system has such trouble keeping illegals out is that it has just as many problems legalizing the immigrants we want.

Take this Catch-22: Immigrants practically can’t work legally in the sectors where there’s greatest demand for their labor.

Consider the work visa – a temporary permit that doesn’t automatically make you eligible for citizenship, but merely lets you work legally in this country for a set period of time (and therefore go overseas and get back in on your return).

But unskilled laborers don’t qualify.

“We get a lot of calls for nannies,” says Nilie Pajoohi, an immigration attorney in New York, “but there is no temporary category for that. People would go through the legal means to hire them but there is no category for foreign-born unskilled labor.”

So even if a contractor, bodega owner or restaurateur wants to sponsor his foreign-born employees’ applications for work permits, he can’t: The existing work-visa categories don’t allow for day laborers, dishwashers or deliverymen.

Work visas – which require employer sponsorship – are now reserved for skilled labor: people who have a bachelors or advanced degrees and those who bring special skills that U.S. employers’ need. Even here, demand far exceeds supply: The annual quota is just 65,000, a limit reached before even eight months had passed this year.

President Bush hopes to tackle these issues with immigration reform. He wants “a new temporary worker program that will match willing foreign workers with willing American employers, when no Americans can be found to fill the jobs.”

Under his plan, new temporary work visas would be valid for three years, and renewable (the White House has yet to specify the limit on renewals). They’d also be portable – not tied to a specific job – so each immigrant could change jobs, even across sectors. Would-be immigrants (and those now here illegally) could apply for a temporary work visa from their home country, with valid proof of a job offer from a U.S. employer.

But Bush’s guest-worker proposal does nothing to address the systemic dysfunction of the immigration bureaucracy.

Back to work visas: Even with current quotas much lower than what Bush envisions, the wait time for approval is tremendous. Immigration attorney Neil Weinrib has clients who’ve been waiting since 1998.

The first step toward work authorization is the Department of Labor (DOL). It approves all employment-based visa applications, then passes them on to the United States Citizenship and Immigration Services (USCIS), which issues the work permit.

DOL has a backlog of 340,000-plus work-visa applications – five years’ worth – some as old as 2001. To fix the mess, it recently split its system in two; one division handles applications filed after March 28 of this year, in an average of 45 to 60 days. The division tackling the backlog doesn’t hope to finish until 2007, so some applicants will have waited seven years.

And, again, that doesn’t finish the process: The application then goes to USCIS – which means more delays.

USCIS wasn’t known for speed back when it was called the Immigration and Naturalization Service. Now it’s part of the Homeland Security Department, and the change (plus increased security concerns, post-9/11, at least at first), made it worse. At the end of 2003, USCIS had 6.2 million applications of all types pending – a jump of 59 percent, or 2.3 million, from the end of 2001.

The long wait for a work permit harms both employee and employer. Employees are in limbo – legally allowed to stay at the job that is sponsoring their permit, but unsure they can get back into the country if they visit home, or need to travel on business – these are high-skilled folks, remember.

And if the employee gets laid off before his work permit comes through, he loses his legal right to be here and will have to go out and find another employer willing to sponsor him. And there are a limited number of sectors of the economy where sponsoring a foreign-born employee is run of the mill.

Then again, this backlog problem is common to all USCIS procedures. Chung-Wha Hong, executive director of the New York Immigration Coalition, says it can now take up to 19 months – a year and a half – just to get a replacement green card, if one is lost or stolen. It used to take one day. “Would we accept it if the Department of Motor Vehicles took that long to get us a driver’s license?” she asked.

President Bush is hoping the Senate will pass a version of his guest-worker proposal. (The House is supposed to deal with tougher border enforcement and security measures.) Unfortunately, he is much less concerned about demanding a cleanup at USCIS. So as reform works its slow, uncertain way through Congress, millions of immigrants – legal immigrants – anxiously await a decision on their applications.